De novo osteogenesis from human ligamentum flavum by adenovirus-mediated bone morphogenetic protein-2 gene transfer

Two novel BMP-2 variants identified in patients with thoracic ossification of the ligamentum flavum

Thoracic ossification of the ligamentum flavum (TOLF)is a common cause of thoracic spinal canal stenosis and has been reported almost exclusively in East Asian countries. In this study, we established a relationship between bone morphogenic protein 2 (BMP-2) and TOLF. We divided patients into two groups according to severity of ossification and identified susceptible loci through exome sequencing. We identified 39 novel likely pathogenic variants in 29 genes in the transforming growth factor-beta (TGF-β) superfamily or TGF-β/BMPs signaling pathway, including two missense variants in BMP-2 (NM_001200.3) exon region, c.460C>G:p.(R154G) and c.584G>T:p.(R195M). Further Sanger sequencing and genotyping suggested the variants were only found in patients with long regional OLF. Bioinformatic assays predicted the two BMP-2 variants to cause significant alterations to gene and protein expression. Functional assays showed upregulation of BMP-2 expression, increased osteogenic marker expression, and enhanced osteogenic differentiation. Collectively, these results suggest a genetic contribution to the pathogenesis of TOLF, particularly in patients with long segment disease, and that nucleotide substitutions associated with increased BMP-2 expression may be involved in TOLF pathogenesis.

Evaluating Osteogenic Potential of Ligamentum Flavum Cells Cultivated in Photoresponsive Hydrogel that Incorporates Bone Morphogenetic Protein-2 for Spinal Fusion

Regenerative medicine is increasingly important in clinical practice. Ligamentum flava (LF) are typically removed during spine-related surgeries. LF may be a source of cells for spinal fusion that is conducted using tissue engineering techniques. In this investigation, LF cells of rabbits were isolated and then characterized by flow cytometry, morphological observation, and immunofluorescence staining. The LF cells were also cultivated in polyethylene (glycol) diacrylate (PEGDA) hydrogels that incorporated bone morphogenetic protein-2 (BMP-2) growth factor, to evaluate their proliferation and secretion of ECM and differentiation in vitro. The experimental results thus obtained that the proliferation, ECM secretion, and differentiation of the PEGDA-BMP-2 group exceeded those of the PEGDA group during the period of cultivation. The mineralization and histological staining results differed similarly. A nude mice model was utilized to prove that LF cells on hydrogels could undergo osteogenic differentiation in vivo. These experimental results also revealed that the PEGDA-BMP-2 group had better osteogenic effects than the PEGDA group following a 12 weeks after transplantation. According to all of these experimental results, LF cells are a source of cells for spinal fusion and PEGDA-BMP-2 hydrogel is a candidate biomaterial for spinal fusion by tissue engineering.

Ectopic osteogenesis of hBMP-2 gene-transduced human bone mesenchymal stem cells/BCB

We determined the feasibility of using scaffolds of adenoviral human BMP2 gene (AdBMP2)-modified human bone marrow mesenchymal stem cells (hBMSCs) and antigen-free bovine cancellous bone (BCB) to construct bone tissue. hMSCs were infected with AdBMP-2. Expression of BMP-2 and alkaline phosphatase confirmed successful secretion of active BMP-2. The osteogenic capability of a composite of AdBMP2-modified hMSCs with BCB was evaluated in athymic mice (group A). BCB (group B), hMSCs/BCB (group C), adenoviral beta-galactosidase genes (Adbetagal)-transfected hMSCs/BCB (group D) were controls. Formation of bone tissue was assessed by histological methods 4 weeks and 8 weeks after implantation. Implanted cells were identified by human Y-chromosome-specific fluorescence in-situ hybridization (FISH). hMSCs differentiated into osteogenic cells, and bone formation was observed. Obvious bone formation was not noted at any time point in control groups. We hypothesize that the described method is a promising method for bone regeneration.

Applications of an athymic nude mouse model of nonhealing critical-sized calvarial defects

Calvarial bone defects are a common clinical scenario in craniofacial surgery. Numerous approaches are used to reconstruct skull defects, and each possesses its own inherent disadvantages. This fact underscores the opportunity to develop a novel method to repair osseous defects in craniofacial surgery. Recent literature strongly suggests that cell-based therapies in the form of regenerative medicine may be a developing paradigm in reconstructive surgery. Although numerous studies have probed osteoprogenitor cells from mice, few have explored the biology of human cells in the setting of osteogenesis in an equally rigorous manner. This study proposes a nude mouse model of critical-sized calvarial defects to study the in vivo biology of human osteoprogenitor cells. Critical-sized 4.0-mm calvarial defects were created in nude mice (n = 15) with a custom trephine drill bit outfitted to a dental drill handpiece. During the craniotomy, the dura mater was spared from injury. Gross inspection, routine histology, and micro-computed tomographic scanning were performed at 2, 4, 8, and 16 weeks postoperatively. There was no calvarial healing in any of the animals by 16 weeks. The dura mater remained intact in all subjects. Gross, histologic, and radiographic assays confirmed these findings. Although several studies have implanted human osteoprogenitor cells in vivo in various animal models, few have documented the appropriate controls or conditions necessary to support the potential to translate benchtop findings into clinical applications. We propose in this study that the nude mouse critical-sized calvarial defect model will be valuable with increasing investigations with human osteoprogenitor cells.